In the article, History and Development of Polybenzimidazole by E. J. Powers and G. A. Serad (presented on Apr. 15-18, 1986 and published in High Performance Polymers: Their Origin and Development), it is disclosed that a polybenzimidazole (PBI) polymer with 27 wt. % phosphoric acid (H3PO4) absorbed (or pick-up) may have utility as a very thermo-oxidatively stable fiber, pages 19-20 and Table XIII. Powers & Serad teach that the phosphonated PBI is made by soaking PBI films in 2% aqueous phosphoric acid, page 20.
Polybenzimidazole fibers, that have been commercially offered up until this time, are sulfonated, i.e., the fibers, after spinning, are treated with 20 wt. % aqueous sulfuric acid (H2SO4) which results in a 24 wt. % APU (Acid Pick-Up) sulfonated PBI fiber (PBI-s). This sulfonated PBI fiber has met with great commercial success in, for example, fire fighter's turnout gear, because it has an LOI (limiting oxygen index, ASTM D2863) of around 41%.
The commercial introduction of phosphonated polybenzimidazole (PBI-p) fiber is currently being explored. PBI-p fibers are discussed in U.S. patent application Ser. No. 15/193,206 filed Jun. 27, 2016, incorporated herein by reference. It is hoped that these new PBI-p fibers will enable a new class of lighter weight fabrics with greater flame-resistant and heat-resistant properties than those fabrics previously commercialized with PBI-s fibers alone. For example, these new PBI-p fabrics may be used in fire fighter's turnout gear. The new fabric may enable the turnout gear to be lighter weight and provide equivalent or better protection for the fire fighters.
In some thermal protective applications, for example, fire fighter's turnout gear, fabrics with less weight but the same or better flame-resistant and/or heat-resistant properties are desired. Currently, when a fire fighter dies in the line of duty, the cause of death is more likely to be some sudden cardiac event brought on by heat stress than death attributable to the actual fire. The heat stress may be reduced by lighter weight garments. But, fire fighters still want the same flame protection. Hence, the search for new fabrics for the garment that weigh less, but have the same or better flame-resistant and/or heat-resistant properties.
Accordingly, there is a need for new fabrics having lighter weights and equivalent or better flame-resistant and/or heat-resistant properties than those currently available, and those new fabrics may be made with PBI-p fibers.